The invention concerns a procedure and an apparatus for determining the extent of the noise level of an electronic object to be measured.
Disclosed by DE 41 22 189 A1 is a procedure and an apparatus for the determination of the noise temperature of an electronic object to be measured. Contrary to the conventional means of procedure up to now, instead of a noise source, a sine signal was input into the measured object and by means of a level meter, the power was measured. The sine-signal source can be toggled between two power levels. These input power levels P1 and P2 are known with great accuracy. During a calibration, first, the inherent noise-power levels P1K and P2K were measured, since the sine-signal source is connected directly to the level meter without an interposed switching of the measured object. When this is carried out, the two connectable power levels P1 and P2 are applied to the sine signal source. During the actual measurement, the same power levels P1 and P2 were connected to the input of the measured object, and the outputs of the measured object were connected to the level meter, whereby, the corresponding power levels P1M and P2M can be read off from the level meter.
In the patent claim 1 of DE 41 22 189 A1 is given a formula for the computation of the noise-temperature TM as related to the magnitude of these measured values. In the numbers of this formula, are found the differences P2M−P2K and P1K−P1M. At this time, the sum of the noise power and the power of that sine signal which is superimposed on the noise signal are measured by the level meter. The then acquired differences differ from zero, as long as the sine signal and the noise signal have approximately the same level. Should however, the sine signal dominate in the superimposed signal mix, then these differences scarcely differ between one another from zero, since these, with the calibration and with the actual measured power level, differ in the noise signal portion. This difference, however, can scarcely be evaluated, in taking the difference because of the dominating portion of the sine signal. The described procedure in DE 41 22 189 A1 is only adaptable when the power portion of the sine signal has the general magnitude of the noise power.
In the practice, however, there is a need, of evaluating measured objects in the activated state. For instance, the noise temperature of an amplifier is of interest not only in stand-by operation, but most surely, also in the case of high modulation, such as is the case with amplifiers in practical operations. To this end, it becomes necessary that the measured object, for instance, an amplifier, by modulated with a sine-signal having a relatively high level, so that the object under measurement is sufficiently modulated for this measurement. Such measurements are, however, not possible with the procedure described in DE 41 22 189 A1, due to the reasons set forth above.
Thus, the invention has the purpose, of making available a procedure and an apparatus for the determination of the degree of noise of an electronic object being measured, which enables a determination of the level of the noise even in the case of high modulation of the object to be measured.